1. Field of the Invention
The present invention relates to a method and an apparatus for manufacturing trichlorosilane by decomposing compounds (hereinbelow, referred to as “polymers”) containing high-boiling chlorosilanes, which are generated in a polycrystalline silicon manufacturing process, a trichlorosilane manufacturing process, or a conversing process. In particular, the present invention relates to a method and an apparatus for manufacturing trichlorosilane by decomposing polymers that have been separated in a chlorination step, polymers that have been separated from an exhaust gas of a polycrystalline silicon reaction step, or polymers that have been separated in a conversion step producing trichlorosilane from silicon tetrachloride in the exhaust gas.
Priority is claimed on Japanese Patent Application No. 2008-201864, filed Aug. 5, 2008, the content of which is incorporated herein by reference.
2. Description of Related Art
The high-purity polycrystalline silicon that can be used as a semiconductor material is mainly manufactured by the Siemens process in which, for example, trichlorosilane (SiHCl3; abbreviated “TCS”) and hydrogen are used as raw materials, a gas mixture thereof is introduced into a reactor and brought into contact with heated silicon rods, and silicon is deposited on the surfaces of the silicon rods due to the hydrogen reduction or thermal decomposition of the trichlorosilane at a high temperature. The high-purity trichlorosilane to be introduced into the reactor, for example, is manufactured by introducing metallurgical grade silicon and hydrogen chloride into a fluidized chlorination reactor to react them, chlorinating the silicon to produce crude TCS (chlorination step), and purifying the crude TCS by distillation into high purity TCS.
In the manufacture of polycrystalline silicon, the reactor exhaust gas includes, in addition to unreacted trichlorosilane and hydrogen chloride, by-products such as silicon tetrachloride (SiCl4; STC) and chlorosilanes including, for example, tetrachlorodisilane (Si2H2Cl4) and hexachlorodisilane (Si2Cl6) (refer to PCT International Publication WO 02/012122). The chlorosilanes having boiling point higher than that of silicon tetrachloride are referred to herein as “high-boiling chlorosilanes”. Trichlorosilane is obtained by distillation of chlorosilanes including trichlorosilane which is generated in the conversion furnace from silicon tetrachloride and hydrogen in the exhaust gas (conversion step), and the trichlorosilane is reused. The gas produced in the chlorination reactor or the conversion furnace includes hydrogen chloride, silicon tetrachloride, and the high-boiling chlorosilanes in addition to trichlorosilane.
Conventionally, polymers which are separated and distilled from produced gas in the chlorination reactor or the conversion furnace and the reactor exhaust gas undergo a hydrolytic process and are then discarded. Thus, there is problem in that the hydrolytic and the waste disposal processes are costly.
A method is known in which the polymers generated in the manufacture of polycrystalline silicon are returned to a fluidized reactor, and then decomposed and used in the manufacture of trichlorosilane (refer to Japanese Unexamined Patent Application, First Publication No. H01-188414). However, in this method, because the silicon powder and polymers supplied to the fluidized reactor are mixed, there is a problem that the fluidity of the silicon powder is reduced and the conversion rate of the silicon powder to chlorosilanes is lowered.